The Doctor at last succeeds in returning Ian and Barbara to 1960s England but a fault occurs during materialisation and the Tardis and its occupants are miniaturised. Emerging into the grooves of some crazy paving, they discover an assortment of “giant” dead insects that have all succumbed to a powerful new insecticide – DN6. A ruthless businessman Forester is determined to manufacture the chemical, even though its effect on the world’s agriculture could be catastrophic. Only the minuscule foursome can stop him, but Barbara has herself become contaminated…

Reducing the time travellers to “miniscules” (sic) was a concept that Doctor Who’s creator Sydney Newman had favoured from the beginning. The original format intended that stories would vary between past, future and “sideways” settings. The first two came to dominate while the other – that of transcending dimensions – was rarely explored. Many months passed before Verity Lambert’s team felt confident enough to tackle the complexities of a “planet of giants”. Her associate producer, Mervyn Pinfield, a seen-it-all BBC pro, was put in charge of directing and largely pulled it off.

“Forget how absurd things are,” urges Ian. Well, we’ll try, Mr Chesterton. And you have to admire their ambition. The outsize sets and props (insects, briefcase, matches, telephone) still look impressive for the period (decades before CGI) and credit must go to Raymond Cusick. His most impressive set is a gigantic sink with plug, chain and plughole that Hartnell and co clamber around on. (We cut to a real sink for one of the series’ most bizarre cliffhangers – bloodied water draining down a plughole.)

It’s unfortunate that despite such positives, the drama itself is less than enthralling. The ecological angle – an insecticide that could have a parlous effect on agriculture – seems ahead of its time now, but the viewer quickly tires of Kray-alike villain Forester, mousey scientist Smithers, and Farrow, the civil servant with whistling dentures. The fact that the “giants” never interact with the “minuscules” is a shame, although there is an effective montage when the Doctor’s group stands in front of Farrow’s corpse with its massive unseeing eyes.

It’s not a great story for Barbara. Besides having to climb over the sets in unflattering slacks, she comes across as uncharacteristically wet. At the sight of a giant cat, she buries her face in Ian’s shoulder. And her plight – DN6 contamination – soon becomes tedious when she repeatedly fails to inform her friends.

Two Doctor Who greats make inauspicious debuts. Maestro from Oz, Dudley Simpson delivers some annoyingly childish music (he’d soon get the knack). And Douglas Camfield, who’d become the BBC’s hottest director in the following decades, got his very first directing job on episode four.

And, yes, I did mean “episode four”. Planet of Giants began life as a four-parter in the first production run but was held back to kick-start season two. Lambert felt the action needed tightening up so she took the extraordinary measure of editing parts three and four into one instalment. Pinfield graciously allowed Camfield to take sole on-screen credit for the new episode three.

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Radio Times archive material

To herald the start of season two, RT led with a one-page feature, updating viewers on the “far, fabulous and wonderfully fantastic” odyssey. It also let its own giant cat out of the bag: “Dr. Who… has not seen the last of the Daleks.”